The present invention relates to a method of examining the coat condition of an inside surface-coated metallic pipe and to an apparatus used for the examination.
In recent years, as a measure to counter the aging of water supply pipes and water drain pipes, a technique to coat the inside surface of pipes by injecting epoxy resin by using air so that they can withstand reuse after the corroded layers of a pipe are removed and ground, has been adopted.
However, since an object distributing pipe system generally forms a complicated system having many branches and bendings, a problem has arisen, namely, certain unpainted portions remain depending on the setting of painting conditions such as the amount of paint.
For this reason, when an uncoated portion remains, it must be detected and coated again. For detecting it, the following methods have been adopted in the past.
First, there is a method in which a fiber scope having flexibility is inserted into the inside of a pipe from the gateway of the pipe, and by visually checking the wall surface inside the pipe, the presence of defects is detected.
Second, there is a method in which an electrode is provided in the tip of a conductor and inserted into the inside of a pipe, then the coat condition is checked by utilizing the instantaneous electric discharge phenomenon.
Third, as shown in FIG. 4, there is a method in which the pipe 41 which is coated with 45 is filled with an electrolytic solution 42, one end of the insulation meter 43 being connected to the pipe 41 on one hand, and the other end of the pipe 43 being connected to the electrode bar 44 inserted into the pipe 41. According to this method, when a defect exists on the coat 45, since the electrolytic solution makes direct contact with the pipe 41, insulation resistance is decreased, thereby enabling the defect to be detected.
In the first method described above, however, in the case of a small 20A (JIS standard) sized pipe or thereabouts, only a scope having about four bendings or less can be inserted. What is more, this operation requires a highly difficult technique. The length that the apparatus can detect is generally about 3 m. In recent years, an apparatus has been produced capable of measuring to the depth of 6 m. It is, however, very expensive, and there is room for improvements in its maneuverability.
In the second method, an examination inside a bent pipe rather than a straight pipe is difficult since the means for inserting an electrode into an intricately bent pipe has not been developed.
In the third method, since the entire pipe 41 must be filled with the electrolytic solution 42, the preparation on a large scale is required. Furthermore, though in the third method, a defect can be detected by a change in an indication of the insulation meter 43, specifying the defect's location is difficult, so such a method cannot be put into practical use.
The present invention has been devised in light of the foregoing problems. It is a technical objective of the present invention to provide a method of examining the coat condition of an inside surface-coated metallic pipe and an apparatus for use in such a method, in which coat defects can be detected easily and reliably even in an intrincately bent pipe, and its position can be determined.